Scrub and dice the sweet potato. Trim the leeks, discarding the dark green parts. Halve the white and light green parts lengthwise, wash thoroughly, and slice crosswise. Toss the sweet potato, leeks, and corn in a baking pan with olive oil, salt, and pepper. Roast until nicely browned, about twenty minutes or maybe longer because of the corn giving off liquid.

Meanwhile, bring the quinoa and water to a boil in a small pot. Reduce heat to low and cook for 15 minutes. Turn off the heat and let it stand. When the vegetables are roasted, add the quinoa right to the baking pan and stir it all together.